What is the minimum depth of footing for a residential structure?
The bottom of exterior footings should extend below the frost line, but not less than 12 inches below the undisturbed soil. Your local building department should be able to provide frost line depth information for your area. Frost line depth can be also determined based on the air-freezing index map. This map and the methodology for determining frost line depth can be found in the HUD publication, Structural Design Loads for One- and Two-Family Dwellings, at www.huduser.org.